1,528 research outputs found
Non-unitary evolution of neutrinos in matter and the leptonic unitarity test
We present a comprehensive study of the three-active plus sterile
neutrino model as a framework for constraining leptonic unitarity violation
induced at energy scales much lower than the electroweak scale. We formulate a
perturbation theory with expansion in small unitarity violating matrix element
while keeping (non- suppressed) matter effect to all orders. We show
that under the same condition of sterile state masses as in vacuum, assuming typical
accelerator based long-baseline neutrino oscillation experiment, one can derive
a very simple form of the oscillation probability which consists only of
zeroth-order terms with the unique exception of probability leaking term
of . We argue, based on our
explicit computation to fourth-order in , that all the other terms are
negligibly small after taking into account the suppression due to the mass
condition for sterile states, rendering the oscillation probability {\em
sterile-sector model independent}. Then, we identify a limited energy region in
which this suppression is evaded and the effects of order corrections may
be observable. Its detection would provide another way, in addition to
detecting , to distinguish between low-scale and
high-scale unitarity violation. We also solve analytically the zeroth-order
system in matter with uniform density to provide a basis for numerical
evaluation of non-unitary neutrino evolution.Comment: 35 content pages + 12 appendix pages, 4 figures; Several clarifying
modifications to match the published versio
Unitarity of the Leptonic Mixing Matrix
We determine the elements of the leptonic mixing matrix, without assuming
unitarity, combining data from neutrino oscillation experiments and weak
decays. To that end, we first develop a formalism for studying neutrino
oscillations in vacuum and matter when the leptonic mixing matrix is not
unitary. To be conservative, only three light neutrino species are considered,
whose propagation is generically affected by non-unitary effects. Precision
improvements within future facilities are discussed as well.Comment: Standard Model radiative corrections to the invisible Z width
included. Some numerical results modified at the percent level. Updated with
latest bounds on the rare tau decay. Physical conculsions unchange
Probing non-unitary mixing and CP-violation at a Neutrino Factory
A low energy non-unitary leptonic mixing matrix is a generic feature of many
extensions of the Standard Model. In such a case, the task of future precision
neutrino oscillation experiments is more ambitious than measuring the three
mixing angles and the leptonic (Dirac) CP-phase, i.e., the accessible
parameters of a unitary leptonic mixing matrix. A non-unitary mixing matrix has
13 parameters that affect neutrino oscillations, out of which four are
CP-violating. In the scheme of Minimal Unitarity Violation (MUV) we analyse the
potential of a Neutrino Factory for determining or constraining the parameters
of the non-unitary leptonic mixing matrix, thereby testing the origin of
CP-violation in the lepton sector.Comment: 21 pages, 8 eps figures, REVTeX
EURONU WP6 2009 yearly report: Update of the physics potential of Nufact, superbeams and betabeams
Many studies in the last ten years have shown that we can measure the unknown
angle theta13, discover leptonic CP violation and determine the neutrino
hierarchy in more precise neutrino oscillation experiments, searching for the
subleading channel nue -> numu in the atmospheric range. In this first report
of WP6 activities the following new results are reviewed: (1) Re-evaluation of
the physics reach of the upcoming generation of experiments to measure theta13
and delta; (2) New tools to explore a larger parameter space as needed beyond
the standard scenario; (3) Neutrino Factory: (a) evaluation of the physics
reach of a Nufact regards sterile neutrinos; (b) evaluation of the physics
reach of a Nufact as regards non-standard interactions; (c) evaluation of the
physics reach of a Nufact as regards violation of unitarity; (d) critical
assessment on long baseline tau-detection at Nufact; (e) new physics searches
at a near detector in a Nufact; (4) Beta-beams: (a) choice of ions and location
for a gamma = 100 CERN-based beta-beam; (b) re-evaluation of atmospheric
neutrino background for the gamma = 100 beta-beam scenario; (c) study of a two
baseline beta-beam; (d) measuring absolute neutrino mass with beta-beams; (e)
progress on monochromatic beta-beams; (5) Update of the physics potential of
the SPL super-beam. Eventually, we present an updated comparison of the
sensitivity to theta13, delta and the neutrino mass hierarchy of several of the
different proposed facilities.Comment: 2009 Yearly report of the Working Package 6 (Physics) of the EUROnu
FP7 EU project. 55 pages, 21 figures
Non-standard interactions versus non-unitary lepton flavor mixing at a neutrino factory
The impact of heavy mediators on neutrino oscillations is typically described
by non-standard four-fermion interactions (NSIs) or non-unitarity (NU). We
focus on leptonic dimension-six effective operators which do not produce
charged lepton flavor violation. These operators lead to particular
correlations among neutrino production, propagation, and detection non-standard
effects. We point out that these NSIs and NU phenomenologically lead, in fact,
to very similar effects for a neutrino factory, for completely different
fundamental reasons. We discuss how the parameters and probabilities are
related in this case, and compare the sensitivities. We demonstrate that the
NSIs and NU can, in principle, be distinguished for large enough effects at the
example of non-standard effects in the --sector, which basically
corresponds to differentiating between scalars and fermions as heavy mediators
as leading order effect. However, we find that a near detector at superbeams
could provide very synergistic information, since the correlation between
source and matter NSIs is broken for hadronic neutrino production, while NU is
a fundamental effect present at any experiment.Comment: 32 pages, 5 figures. Final version published in JHEP. v3: Typo in Eq.
(27) correcte
Indirect unitarity violation entangled with matter effects in reactor antineutrino oscillations
If finite but tiny masses of the three active neutrinos are generated via the
canonical seesaw mechanism with three heavy sterile neutrinos, the 3\times 3
Pontecorvo-Maki-Nakagawa-Sakata neutrino mixing matrix V will not be exactly
unitary. This kind of indirect unitarity violation can be probed in a precision
reactor antineutrino oscillation experiment, but it may be entangled with
terrestrial matter effects as both of them are very small. We calculate the
probability of \overline{\nu}_e \to \overline{\nu}_e oscillations in a good
analytical approximation, and find that, besides the zero-distance effect, the
effect of unitarity violation is always smaller than matter effects, and their
entanglement does not appear until the next-to-leading-order oscillating terms
are taken into account. Given a 20-kiloton JUNO-like liquid scintillator
detector, we reaffirm that terrestrial matter effects should not be neglected
but indirect unitarity violation makes no difference, and demonstrate that the
experimental sensitivities to the neutrino mass ordering and a precision
measurement of \theta_{12} and \Delta_{21} \equiv m^2_2 - m^2_1 are robust.Comment: 21 pages, 6 figures, version to be published in PLB, more discussions
adde
Mass and Flavor Mixing Schemes of Quarks and Leptons
We give an overview of recent progress in the study of fermion mass and
flavor mixing phenomena. The hints exhibited by the quark and lepton mass
spectra towards possible underlying flavor symmetries, from which realistic
models of mass generation could be built, are emphasized. A variety of schemes
of quark mass matrices at low and superhigh energy scales are described, and
their consequences on flavor mixing and CP violation are discussed. Instructive
patterns of lepton mass matrices, which can naturally lead to large flavor
mixing angles, are explored to interpret current data on atmospheric and solar
neutrino oscillations. We expect that B-meson factories and long-baseline
neutrino experiments will soon shed more light on the dynamics of fermion
masses, flavor mixing and CP violation.Comment: LaTex 81 pages. Minor changes made, typing errors corrected, and
references added. Prog. Part. Nucl. Phys. (in printing
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